A transmission mounted in a vehicle is provided with a rotary shaft for transmitting drive power as represented by an input shaft by which drive power output from a drive source, such as an engine or electric motor, or the like, is input, and an output shaft which outputs drive power transmitted from the input shaft, to a differential device, or the like. Transmission gears are provided on these rotary shafts, and in the case of a manual transmission, a synchronization device which synchronizes the rotary shaft rotation and the transmission gear rotation is also provided.
Furthermore, in the case of a manual transmission, lubricating oil is supplied to parts requiring lubrication, such as the gaps between the rotary shafts of the transmission and the gears which fit freely on the rotary shafts, the coupling portion (indexing section) between the hub and the synchronizer ring in the synchronization device, and the like, in order to reduce friction and suppress abnormal noise. In a known lubrication structure for supplying lubricating oil to these parts requiring lubrication, lubricating oil inside the transmission case taken up by rotation of a ring gear of the differential device which is provided in an integrated fashion with the transmission, and some transmission gears, is received in an oil path, and passes from the oil path and through an in-case oil passage, or the like, to an oil passage inside the rotary shaft, from where the lubricating oil is supplied to the parts requiring lubrication outside the rotary shaft.
In a lubrication structure of this type, a main oil passage extending in an axial direction from one end of the rotary shaft of the transmission, and a plurality of subsidiary oil passages extending in radial directions and communicating with the main oil passage and an outer circumferential section of the rotary shaft, are formed inside the rotary shaft. Furthermore, the positions of the subsidiary oil passages in the axial direction are set in accordance with the positions of the parts requiring lubrication. According to this lubrication structure, it is possible to supply lubricating oil that has been introduced into the main oil passage, to the respective parts requiring lubrication on the outside of the rotary shaft, via the subsidiary oil passages.
However, in a lubricating structure of this type, since the distance from the entrance of the main oil passage to the entrance of the subsidiary oil passage differs, for each subsidiary oil passage, then there is a problem in that a relatively large amount of lubricating oil is supplied to the subsidiary oil passages which are relatively close to the entrance of the main oil passage, and the amount of lubricating oil supplied becomes less in subsidiary oil passages which are relatively distant from the entrance of the main oil passage. Consequently, in some driving states, insufficient lubrication is liable to occur in parts requiring lubrication corresponding to subsidiary oil passages which are distant from the entrance of the main oil passage. One example of a state where a problem of insufficient lubrication of this kind can readily occur is a state where the transmission is in neutral, so the ring gear of the differential device does not rotate and hence taking up of the lubricating oil due to the rotation of the ring gear cannot be expected to occur.
In view of this problem, Patent Document 1 discloses a structure for guiding lubricating oil to a plurality of subsidiary oil passages extending in radial directions from a main oil passage extending in an axial direction, inside a rotary shaft of a manual transmission, wherein lubricating oil is also supplied satisfactorily to subsidiary oil passages which are distant from an entrance of the main oil passage.
More specifically, in the technology in Patent Document 1, a tubular resin member constituting a main oil passage is fitted into an oil hole extending in an axial direction formed inside the rotary shaft of the transmission, in such a manner that lubricating oil introduced into an entrance section at one end portion of the resin member is guided via an inclined oil passage formed in a circumferential wall section of the resin member to a subsidiary oil passage provided in the rotary shaft so as to extend in a radial direction. A plurality of subsidiary oil passages of the rotary shaft are provided at mutually different positions in the axial direction, and an inclined oil passage is provided in the resin member respectively for each of the subsidiary oil passages. The respective inclined oil passages are provided so as to be inclined outwards in radial directions, towards the downstream side in the axial direction. Furthermore, the entrances of the inclined oil passages are provided in a circumferential edge section of the entrance section of one end portion of the resin member, and the exits of the inclined oil passages are provided on an outer circumference surface of the resin member, at positions communicating with the entrances of the subsidiary oil passages.
According to the technology of Patent Document 1, the lubricating oil introduced into the entrance section at one end portion of the resin member is guided to the entrances of the inclined oil passages by the centrifugal force created by the rotation of the rotary shaft, and by utilizing the inclination of the inclined oil passages and the centrifugal force created by the rotation of the rotary shaft, the lubricating oil introduced into the inclined oil passages is guided to the exits of the inclined oil passage and is introduced into the subsidiary oil passages of the rotary shaft which are communicated with the exits of the inclined oil passages. Consequently, the lubricating oil is supplied individually to the subsidiary oil passages via the respectively corresponding inclined oil passages, and therefore it is possible to supply the lubricating oil in substantially uniform fashion to the subsidiary oil passages and hence to the respective parts requiring lubrication corresponding to the subsidiary oil passages, irrespective of the positions of the subsidiary oil passages in the axial direction.
However, in the technology in Patent Document 1, it is, necessary to form the inclined oil passages in the resin member so as to be inclined outwards in radial directions towards the downstream side with respect to the axial direction, as described above, in order to guide the lubricating oil to the subsidiary oil passages of the rotary shaft, and therefore the entrances of the inclined oil passages are disposed towards the inner side in the radial direction, compared to the exits of the inclined oil passages.
Accordingly, the entrance sections at the end portion of the resin member are narrow, and therefore the amount of lubricating, oil introduced into the entrance sections is decreased. Consequently, the amount of lubricating oil supplied to the parts requiring lubrication via the subsidiary oil passages is also decreased, and there is a drawback in that the effect in suppressing insufficient lubrication described above is not necessarily adequate.
Conversely, in the technology in Patent Document 1, if it is sought to maintain the introduced amount of lubricating oil by maintaining the internal diameter of the entrance sections in one end portion of the resin member, then it is necessary to increase the outer diameter of the resin member. Consequently, in this case, the increase in the diameter of the rotary shaft gives rise to an increase in the size of the transmission.
Furthermore, this problem is not limited to a manual transmission but also occurs similarly in an automatic transmission or continuously variable transmission, provided that the transmission has a plurality of parts requiring lubrication at different positions in the axial direction on the outer circumferential section of a rotary shaft.
Patent Document 1: Japanese Patent Application Publication No. 2012-52649